A. Field of the Invention
The device of the present invention generally relates to a molded case circuit breaker and, more particularly, to an improved internal venting system for a molded case circuit breaker.
B. Description of the Prior Art
Circuit breakers and, more particularly molded case circuit breakers are old and well known in the prior art. Examples of such devices are disclosed in U.S. Pat. Nos. 2,186,251; 2,492,009; 3,239,638; 3,525,959; 3,590,325; 3,614,685; 3,775,713; 3,783,423; 3,805,199; 3,815,059; 3,863,042; 3,959,695; 4,077,025; 4,166,205; 4,258,403; and 4,295,025. In general, prior art molded case circuit breakers have been provided with movable contact arrangements and operating mechanisms designed to provide protection for an electrical circuit or system against electrical faults, specifically, electrical overload conditions, low level short circuit or fault current conditions, and, in some cases, high level short circuit or fault current conditions. Prior art devices have utilized an operating mechanism having a trip mechanism for controlling the movement of an overcenter toggle mechanism to separate a pair of electrical contacts upon an overload condition or upon a short circuit or fault current condition. Such trip mechanisms have included a bimetal movable in response to an overload condition to rotate a trip bar to open a pair of electrical circuit breaker contacts. Such prior art devices have also utilized an armature movable in response to the flow of short circuit or fault current similarly to rotate the trip bar to cause the pair of contacts to separate. A significant problem in providing high interrupting capacities in a dimensionally small circuit breaker is controlling the internal gas pressure increase and expansion which occurs during arc interruption. Structural damage to the molded case breaker can result from such gas pressure increase. The arc gases can be allowed to expand internally in order to control the pressure increase, however, this internal expansion is limited by the physical volume available, the physical configurations and dispositions of the internal components of the circuit breaker and the desired interrupting performance characteristics.
While many prior art devices have provided adequate protection against fault conditions in an electrical circuit, a need exists for dimensionally small molded case circuit breakers capable of fast, effective and reliable operation and, more specifically, for components thereof that are designed for controlling the internal gas pressure increase and expansion during an arc interruption.